Field of the Invention
The present invention relates to an image forming apparatus, an image forming system and an image forming method capable of printing a front-and-back adjustment mark outside an image forming area of a transfer medium by an image forming unit and adjusting the front and back in image formation by an image read result of the front-and-back adjustment mark.
Description of the Related Art
In an image forming apparatus, an image is formed on a paper sheet based on image data, and a cutting mark such as a register mark is sometimes printed as an additional image in a margin part outside an image area of the paper sheet as a mark when cutting the paper sheet (for example, see Japanese Patent Laid-Open No. 2011-11367).
In addition, in the image forming apparatus, an image can be formed on both surfaces of the paper sheet by providing a duplex printing mechanism. The duplex printing mechanism is normally a mechanism that inverts and conveys a paper sheet body on one surface of which an image is formed and conveys the paper sheet body to a conveyance direction upstream side of the image forming unit. Now, when performing duplex printing, the paper sheet sometimes moves through a conveyance path different from the one in the case of normal simplex printing only, and positional displacement of the image is sometimes generated between a front surface and a back surface. Also, between the front surface and the back surface, the paper sheet is expanded and contracted due to presence/absence of temperature rise and humidification or the like, and a size of the image sometimes changes. Therefore, an image forming apparatus capable of front-and-back adjustment of adjusting positions of the image on the front and the back and magnifications on the front and the back has been proposed.
In the front-and-back adjustment, a mark for image position adjustment (for example, a cross patch) is printed on the front and back surfaces of a paper sheet, it is image-detected in an inline detection unit, and image formation adjustment is performed.
For example, in Japanese Patent Laid-Open No. 2014-22919, a device that matches the front and back by using a chart exclusive for front-and-back positioning is proposed.
In addition, in Japanese Patent Laid-Open No. 2006-91179, an image adjustment pattern is formed outside an image area and it is read to adjust the front and back.
Now, in an image forming apparatus, there is a demand to perform real time adjustment of adjusting the front and back during a job. However, in the apparatus disclosed in Japanese Patent Laid-Open No. 2014-22919, since an exclusive chart is utilized, there is a problem that waste paper is generated. In addition, when cutting a paper sheet on which an image is printed, an additional image different from a normal image is sometimes printed in a margin or the like such as printing a cutting mark as a mark for cutting. When this function is used, there is a merit that the front and back are not shifted from a leading page to a final page, and there is no shift during cutting. However, when such an additional image is printed in coexistence with a mark for image position adjustment as indicated in Japanese Patent Laid-Open No. 2006-91179, it becomes difficult to distinguish both, and there is a risk of causing a cutting error, for example.
In the meantime, in Japanese Patent Laid-Open No. 2011-11367, a cutting mark is printed, and it is conceivable to use it as a front-and-back adjustment mark. However, the cutting mark is made near an input image according to a cutting position, and there is a risk that measurement accuracy during the front-and-back adjustment lowers.